The present invention is in the field of catalyst cores which are especially adapted for use with automotive vehicles to control the chemistry of exhaust emissions. Since the early 1970's, manufacturers of automotive vehicles powered by internal combustion engines whether of the spark ignited or compression ignited type, have been required to treat the exhaust gases from such engines in such a manner as to eliminate undesirable atmosphere polluting chemicals such as unburned hydrocarbons, carbon monoxide, nitrogen oxides, and the like. Up to the present time, this has been achieved largely with catalytic converters which are composed of a shell and one or more catalytic cores contained therein. The catalytic core has, for the most part been a extruded ceramic core having a plurality of longitudinally extending holes therethrough much like a honeycomb. On the interior surfaces of the honeycomb there has been deposited a suitable catalytic material which on contacting exhaust gases at the elevated temperatures thereof reduces or eliminates the undesirable chemicals contained in the exhaust gases.
More recently, and for reasons of economy and durability efforts have been made to utilize as a catalytic support, thin metal strips which are corrugated in a manner such as when wound they provide continuous apertures extending through the length of the core. In such devices, it is essential that the corrugated metal not "nest" whereby well defined ports or openings are closed off. The inner surface of the openings is coated with a catalyst such as palladium or platinum or a combination thereof, which catalysts act in the environment to convert carbon monoxide, for example to carbon dioxide, to enchance the burning of unburned hydrocarbons, and to convert nitrous oxides to nitrogen and oxygen.
The wound, or in some cases folded, metal catalyst supports introduce a problem not experienced with cast ceramic supports. Because of the extreme number of pulsations to which such thin metal foil catalyst support is submitted in the course of its use, such wound or folded metal catalyst supports tend to move in response to such pulsation whereby convolutions of spirally wound thin metal catalyst support, or adjacent folds of a folded catalyst support, for example, will move axially in response to the pulsing flow of gases in an exhaust pipe. Such telescoping of the catalyst support eventually destroys the mechanical integrity of the device.
The present invention provides a method for solving the problem of axial translation of convolutions of a spirally wound thin metal catalyst support.
Reference may be had to the patents to Retallick U.S. Pat. No. 4,301,039; 4,350,617; 4,402,871 which disclose various forms of metal foil configurations for supporting a catalyst material. Referance may also be had to U.S. Pat. No. 4,300,956 which discloses cowound interelated layers of corrugated and noncorrugated Fecralloy Sheets. U.S. Pat. No. 4,318,888 discloses a wound corrugated metal foil wherein one surface carries a platinum catalyst and the facing surface separately carries a palladium catalyst for concurrently treating gases flowing therethrough. Such metal foils or combined foils may be used in the practice of the present invention and accordingly the disclosures of those patents are incorporated herein by reference.
Various means for locking in place folded or spirally wound metal foil supported catalyst members have been suggested including projections extending inwardly from the housing to engage slots or the like in the foil bodies. However, these are not entirely satisfactory and very often reduce the open area as, for example, in the case of a grid or spider disposed transversely of the housing and in contact with each end of the catalyst body.
I have now found that axial translation of convolutions of a spirally wound thin metal foil catalyst carrier can be prevented by conducting such winding about a mandrel having a special and novel configuration. The final wound product has a configuration as a result of winding under tension about a mandrel of the present invention which is oval on each end and circular in the center, the major and minor axes of one end being displaced angularly from the major and minor axes of the opposite end.